This invention relates to a cell washing apparatus and, in particular, to a cell washing apparatus wherein the sample tube holders are provided with radially inwardly directed retaining arms.
A cell washing apparatus is a device adapted to wash a suspension of particles, such as blood cells, with a washing solution. A cell washing apparatus typically includes a rotor having a central shaft or spindle through which the axis of rotation extends. The spindle has a holding plate attached thereon. To the holding plate is pivotally attached an array of sample tube holders. Each of the sample tube holders receives a sample tube carrying a sample which includes the particles to be washed. A hemispherical bowl having an annular retaining lip surrounds the lower end of the rotating spindle.
During the cell packing cycle, as the rotor is rotated, the sample holders pivot radially outwardly under the influence of centrifugal force such that the lower end of each of the sample tubes is inclined in a radially outward direction i.e., the axis of each of the tubes defines a positive angle with respect to the axis of the spindle. The magnitude of the angle defined between the axis of the sample tubes with respect to the axis of rotation of the rotor is limited by the abutment of the lower end of the sample tube holders against the lip on the bowl. While the sample tubes are being rotated a suitable cell washing solution is pumped into the open top of each sample tube. The sample cells move through the washing solution under the influence of centrifugal force and become packed at the bottom of the sample tube.
After the packing cycle is completed the rotor is stopped and the axes of the sample tubes assume a negative angle orientation wherein the lower ends of the sample tubes lie closer to the axis of rotation than do the upper ends. While in this orientation a retaining ring is brought into engagement with the lower end of each of the sample tube holders to hold the lower ends of the tubes in the radially inwardly orientation. The rotor is again rotated and the washing solution is purged from the tubes. The packing and purge cycle are repeated as often as desired.
It has been found that after repeated use the bowl has a tendency to exhibit fatigue cracks. This cracking is believed to be caused by the washing solution settling on the bowl as the solution is purged from the sample tubes during the purge cycle. Fatigue cracking of the bowl is believed to be disadvantageous in that it weakens the bowl and increases the possibility of rotor failure.
It is therefore believed advantageous to provide a cell washing apparatus wherein the bowl may be eliminated but the restraining function performed by the lip on the bowl may be retained.